Procedure for non synchronized radio access (NSRA) resource assignment

ABSTRACT

A procedure for RACH initial access in a mobile terminal is provided such that necessary information is conveyed the for the initial access procedure with less overhead. The method allow an accurate choice of the uplink transport format by allowing the mobile terminal to determine by itself whether a certain transport format may be used for the transmission of a message prior to the first preamble transmission and prior to the power ramping.

CROSS-REFERENCE TO RELATED APPLICATIONS

Pursuant to 35 U.S.C. §120, this application claims the benefit of U.S.Provisional Application Ser. No. 60/862,717 filed on Oct. 24, 2006, thecontents of which is hereby incorporated by reference herein in itsentirety.

FIELD OF THE INVENTION

The present invention is directed to a RACH initial access procedure ina UE, and particularly, to a method for conveying the informationnecessary for the initial access procedure with less overhead.

DESCRIPTION OF THE RELATED ART

Universal mobile telecommunications system (UMTS) is a 3rd Generation(3G) asynchronous mobile communication system operating in wideband codedivision multiple access (WCDMA) based on European systems, globalsystem for mobile communications (GSM) and general packet radio services(GPRS). The long-term evolution (LTE) of UMTS is under discussion by the3rd generation partnership project (3GPP) that standardized UMTS.

The 3GPP LTE is a technology for enabling high-speed packetcommunications. Many schemes have been proposed for the LTE objectiveincluding those that aim to reduce user and provider costs, improveservice quality, and expand and improve coverage and system capacity.The 3G LTE requires reduced cost per bit, increased serviceavailability, flexible use of a frequency band, a simple structure, anopen interface, and adequate power consumption of a terminal as anupper-level requirement.

FIG. 1 is a block diagram illustrating network structure of an evolveduniversal mobile telecommunication system (E-UMTS). The E-UMTS may bealso referred to as an LTE system. The communication network is widelydeployed to provide a variety of communication services such as voiceand packet data.

As illustrated in FIG. 1, the E-UMTS network includes an evolved UMTSterrestrial radio access network (E-UTRAN), an Evolved Packet Core (EPC)and one or more user equipment. The E-UTRAN may include one or moreevolved NodeB (eNodeB) 20, and a plurality of user equipment (UE) 10 maybe located in one cell. One or more E-UTRAN mobility management entity(MME)/system architecture evolution (SAE) gateways 30 may be positionedat the end of the network and connected to an external network.

As used herein, “downlink” refers to communication from eNodeB 20 to UE10, and “uplink” refers to communication from the UE to an eNodeB. UE 10refers to communication equipment carried by a user and may be also bereferred to as a mobile station (MS), a user terminal (UT), a subscriberstation (SS) or a wireless device.

An eNodeB 20 provides end points of a user plane and a control plane tothe UE 10. MME/SAE gateway 30 provides an end point of a session andmobility management function for UE 10. The eNodeB and MME/SAE gatewaymay be connected via an S1 interface.

The eNodeB 20 is generally a fixed station that communicates with a UE10, and may also be referred to as a base station (BS) or an accesspoint. One eNodeB 20 may be deployed per cell. An interface fortransmitting user traffic or control traffic may be used between eNodeBs20.

The MME provides various functions including distribution of pagingmessages to eNodeBs 20, security control, idle state mobility control,SAE bearer control, and ciphering and integrity protection of non-accessstratum (NAS) signaling. The SAE gateway host provides assortedfunctions including termination of U-plane packets for paging reasons,and switching of the U-plane to support UE mobility. For clarity MME/SAEgateway 30 will be referred to herein simply as a “gateway,” but it isunderstood that this entity includes both an MME and an SAE gateway.

A plurality of nodes may be connected between eNodeB 20 and gateway 30via the S1 interface. The eNodeBs 20 may be connected to each other viaan X2 interface and neighboring eNodeBs may have a meshed networkstructure that has the X2 interface.

FIG. 2 is a block diagram depicting architecture of a typical E-UTRANand a typical EPC. As illustrated, eNodeB 20 may perform functions ofselection for gateway 30, routing toward the gateway during a RadioResource Control (RRC) activation, scheduling and transmitting of pagingmessages, scheduling and transmitting of Broadcast Channel (BCCH)information, dynamic allocation of resources to UEs 10 in both uplinkand downlink, configuration and provisioning of eNodeB measurements,radio bearer control, radio admission control (RAC), and connectionmobility control in LTE_ACTIVE state. In the EPC, and as noted above,gateway 30 may perform functions of paging origination, LTE-IDLE statemanagement, ciphering of the user plane, System Architecture Evolution(SAE) bearer control, and ciphering and integrity protection ofNon-Access Stratum (NAS) signaling.

FIGS. 3( a) and 3(b) are block diagrams depicting the user-planeprotocol and the control-plane protocol stack for the E-UMTS. Asillustrated, the protocol layers may be divided into a first layer (L1),a second layer (L2) and a third layer (L3) based upon the three lowerlayers of an open system interconnection (OSI) standard model that iswell known in the art of communication systems.

The physical layer, the first layer (L1), provides an informationtransmission service to an upper layer by using a physical channel. Thephysical layer is connected with a medium access control (MAC) layerlocated at a higher level through a transport channel, and data betweenthe MAC layer and the physical layer is transferred via the transportchannel. Between different physical layers, namely, between physicallayers of a transmission side and a reception side, data is transferredvia the physical channel.

The MAC layer of Layer 2 (L2) provides services to a radio link control(RLC) layer (which is a higher layer) via a logical channel. The RLClayer of Layer 2 (L2) supports the transmission of data withreliability. It should be noted that the RLC layer illustrated in FIGS.3( a) and 3(b) is depicted because if the RLC functions are implementedin and performed by the MAC layer, the RLC layer itself is not required.The PDCP layer of Layer 2 (L2) performs a header compression functionthat reduces unnecessary control information such that data beingtransmitted by employing Internet protocol (IP) packets, such as IPv4 orIPv6, can be efficiently sent over a radio (wireless) interface that hasa relatively small bandwidth.

A radio resource control (RRC) layer located at the lowest portion ofthe third layer (L3) is only defined in the control plane and controlslogical channels, transport channels and the physical channels inrelation to the configuration, reconfiguration, and release of the radiobearers (RBs). Here, the RB signifies a service provided by the secondlayer (L2) for data transmission between the terminal and the UTRAN.

As illustrated in FIG. 3( a), the RLC and MAC layers (terminated in aneNodeB 20 on the network side) may perform functions such as Scheduling,Automatic Repeat Request (ARQ), and Hybrid Automatic Repeat Request(HARQ). The PDCP layer (terminated in eNodeB 20 on the network side) mayperform the user plane functions such as header compression, integrityprotection, and ciphering.

As illustrated in FIG. 3( b), the RLC and MAC layers (terminated in aneNodeB 20 on the network side) perform the same functions as for thecontrol plane. As illustrated, the RRC layer (terminated in an eNodeB 20on the network side) may perform functions such as broadcasting, paging,RRC connection management, Radio Bearer (RB) control, mobilityfunctions, and UE measurement reporting and controlling. The NAS controlprotocol (terminated in the MME of gateway 30 on the network side) mayperform functions such as a SAE bearer management, authentication,LTE_IDLE mobility handling, paging origination in LTE_IDLE, and securitycontrol for the signaling between the gateway and UE 10.

The NAS control protocol may use three different states; first, aLTE_DETACHED state if there is no RRC entity; second, a LTE_IDLE stateif there is no RRC connection while storing minimal UE information; andthird, an LTE_ACTIVE state if the RRC connection is established. Also,the RRC state may be divided into two different states such as aRRC_IDLE and a RRC_CONNECTED.

In RRC_IDLE state, the UE 10 may receive broadcasts of systeminformation and paging information while the UE specifies aDiscontinuous Reception (DRX) configured by NAS, and the UE has beenallocated an identification (ID) which uniquely identifies the UE in atracking area. Also, in RRC-IDLE state, no RRC context is stored in theeNodeB.

In RRC_CONNECTED state, the UE 10 has an E-UTRAN RRC connection and acontext in the E-UTRAN, such that transmitting and/or receiving datato/from the network (eNodeB) becomes possible. Also, the UE 10 canreport channel quality information and feedback information to theeNodeB.

In RRC_CONNECTED state, the E-UTRAN knows the cell to which the UE 10belongs. Therefore, the network can transmit and/or receive data to/fromUE 10, the network can control mobility (handover) of the UE, and thenetwork can perform cell measurements for a neighboring cell.

In RRC_IDLE mode, the UE 10 specifies the paging DRX (DiscontinuousReception) cycle. Specifically, the UE 10 monitors a paging signal at aspecific paging occasion of every UE specific paging DRX cycle.

The paging occasion is a time interval during which a paging signal istransmitted. The UE 10 has its own paging occasion.

A paging message is transmitted over all cells belonging to the sametracking area. If the UE 10 moves from one tracking area to anothertracking area, the UE will send a tracking area update message to thenetwork to update its location.

A physical channel transfers signaling and data between layer L1 of a UEand eNB. As illustrated in FIG. 4, the physical channel transfers thesignaling and data with a radio resource, which consists of one or moresub-carriers in frequency and one more symbols in time.

One sub-frame, which is 1.0 ms. in length, consists of several symbols.The particular symbol(s) of the sub-frame, such as the first symbol ofthe sub-frame, can be used for the L1/L2 control channel. The L1/L2control channel carries L1/L2 control information, such as signaling.

A transport channel transfers signaling and data between the L1 and MAClayers. A physical channel is mapped to a transport channel.

Downlink transport channel types include a Broadcast Channel (BCH), aDownlink Shared Channel (DL-SCH), a Paging Channel (PCH) and a MulticastChannel (MCH). The BCH is used for transmitting system information. TheDL-SCH supports HARQ, dynamic link adaptation by varying the modulation,coding and transmit power, and both dynamic and semi-static resourceallocation. The DL-SCH also may enable broadcast in the entire cell andthe use of beamforming. The PCH is used for paging a UE. The MCH is usedfor multicast or broadcast service transmission.

Uplink transport channel types include an Uplink Shared Channel (UL-SCH)and Random Access Channel(s) (RACH). The UL-SCH supports HARQ anddynamic link adaptation by varying the transmit power and potentiallymodulation and coding. The UL-SCH also may enable the use ofbeamforming. The RACH is normally used for initial access to a cell.

The MAC sublayer provides data transfer services on logical channels. Aset of logical channel types is defined for different data transferservices offered by MAC. Each logical channel type is defined accordingto the type of information transferred.

Logical channels are generally classified into two groups. The twogroups are control channels for the transfer of control planeinformation and traffic channels for the transfer of user planeinformation.

Control channels are used for transfer of control plane informationonly. The control channels provided by MAC include a Broadcast ControlChannel (BCCH), a Paging Control Channel (PCCH), a Common ControlChannel (CCCH), a Multicast Control Channel (MCCH) and a DedicatedControl Channel (DCCH). The BCCH is a downlink channel for broadcastingsystem control information. The PCCH is a downlink channel thattransfers paging information and is used when the network does not knowthe location cell of a UE. The CCCH is used by UEs having no RRCconnection with the network. The MCCH is a point-to-multipoint downlinkchannel used for transmitting MBMS control information from the networkto a UE. The DCCH is a point-to-point bi-directional channel used by UEshaving an RRC connection that transmits dedicated control informationbetween a UE and the network.

Traffic channels are used for the transfer of user plane informationonly. The traffic channels provided by MAC include a Dedicated TrafficChannel (DTCH) and a Multicast Traffic Channel (MTCH). The DTCH is apoint-to-point channel, dedicated to one UE for the transfer of userinformation and can exist in both uplink and downlink. The MTCH is apoint-to-multipoint downlink channel for transmitting traffic data fromthe network to the UE.

Uplink connections between logical channels and transport channelsinclude a DCCH that can be mapped to UL-SCH and a DTCH that can bemapped to UL-SCH. Downlink connections between logical channels andtransport channels include a BCCH that can be mapped to BCH, a PCCH thatcan be mapped to PCH, a DCCH that can be mapped to DL-SCH, and a DTCHthat can be mapped to DL-SCH.

It is known that different cause values may be mapped on the signaturesequence used to send messages between a UE and eNB and that eitherChannel Quality Indicator (CQI) or path loss and cause or message sizeare candidates for inclusion in the initial preamble. FIG. 5 illustratesdifferent messages exchanged between a UE and eNB during initial access.

When a UE wishes to access the network and determines a message to betransmitted, the message may be linked to a purpose and a cause valuemay be determined. The size of the ideal message number 3 illustrated inFIG. 5 may also be determined by identifying all optional informationand different alternative sizes, such as by removing optionalinformation, or an alternative “scheduling request” message may be used.

The UE acquires necessary information for the transmission of thepreamble, UL interference, Pilot Transmit power and requiredSignal-to-Noise Ratio (SNR) for the preamble detection at the receiveror combinations thereof. This information must allow the calculation ofthe initial transmit power of the preamble. It is beneficial to transmitthe uplink message in the vicinity of the preamble from a frequencypoint of view in order to ensure that the same channel is used for thetransmission of the message.

The UE should take into account the uplink interference and the uplinkpath loss in order to ensure that the network receives the preamble witha minimum SNR. The uplink interference can be determined only in theENodeB and, therefore, must be broadcast by the ENodeB and received bythe UE prior to the transmission of the preamble. The uplink path losscan be considered to be similar to the downlink path loss and can beestimated by the UE from the received Rx (receiver) signal strength whenthe transmit power of some pilot sequence of the cell is known to theUE.

The required uplink SNR for the detection of the preamble wouldtypically depend on the NodeB configuration, such as a number of Rxantennas and receiver performance. There may be advantages totransmitting the rather static Transmit power of the pilot and thenecessary uplink SNR separately form the varying uplink interference andpossibly the power offset required between the preamble and the message.

The initial transmission power of the preamble can be roughly calculatedaccording to the following formula:Transmit power=TransmitPilot−RxPilot+ULInterference+Offset+SNRRequired.

Therefore, any combination of SNRRequired, ULInterference, TransmitPilotand Offset can be broadcast. In principle, only one value must bebroadcast. This is essentially the method in current UMTS systems,although the UL interference in LTE will mainly be neighboring cellinterference that is probably more constant than in UMTS.

The UE determines the initial uplink transmit power for the transmissionof the preamble as explained above. The receiver in the eNB is able toestimate the absolute received power as well as the relative receivedpower compared to the interference in the cell. The eNB will consider apreamble detected if the received signal power compared to theinterference is above an eNB known threshold.

The UE performs power ramping in order to ensure that a UE can bedetected even if the initially estimated transmission power for thepreamble is not adequate. Another preamble will most likely betransmitted if no acknowledgement or a negative acknowledgement isreceived by the UE before the next random access attempt. The transmitpower of the preamble can be increased, and/or the preamble can betransmitted on a different uplink frequency in order to increase theprobability of detection. Therefore, the actual transmit power of thepreamble that will be detected does not necessarily correspond to theinitial transmit power of the preamble as initially calculated by theUE.

The UE must determine the possible uplink transport format The transportformat, which may include Modulation and Coding Scheme (MCS) and anumber of resource blocks that should be used by the UE, depends mainlyon two parameters, specifically the SNR at the eNB and the required sizeof the message to be transmitted.

In practice, a maximum UE message size, or payload, and a requiredminimum SNR correspond to each transport format. In UMTS, the UEdetermines before the transmission of the preamble whether a transportformat can be chosen for the transmission according to the estimatedinitial preamble transmit power, the required offset between preambleand the transport block, the maximum allowed or available UE transmitpower, a fixed offset and additional margin. The preamble in UMTS neednot contain any information regarding the transport format selected bythe UE since the network does not need to reserve time and frequencyresources and, therefore, the transport format is indicated togetherwith the transmitted message.

The eNB must be aware of the size of the message that the UE intends totransmit and the SNR achievable by the UE in order to select the correcttransport format upon reception of the preamble and then reserve thenecessary time and frequency resources. Therefore, the eNB cannotestimate the SNR achievable by the UE according to the received preamblebecause the UE transmit power compared to the maximum allowed orpossible UE transmit power is not known to the eNB, given that the UEwill most likely consider the measured path loss in the downlink or someequivalent measure for the determination of the initial preambletransmission power.

The eNB could calculate a difference between the path loss estimated inthe downlink compared and the path loss of the uplink. However, thiscalculation is not possible if power ramping is used and the UE transmitpower for the preamble does not correspond to the initially calculatedUE transmit power. Furthermore, the precision of the actual UE transmitpower and the transmit power at which the UE is intended to transmit isvery low. Therefore, it has been proposed to code the path loss or CQIestimation of the downlink and the message size or the cause value inthe uplink in the signature.

SUMMARY OF THE INVENTION

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. It is to beunderstood that both the foregoing general description and the followingdetailed description of the present invention are exemplary andexplanatory and are intended to provide further explanation of theinvention as claimed.

In one aspect of the present invention, a method of establishing acommunication link between a mobile terminal and a network is provided.The method includes identifying at least two groupings of signatures foraccessing the network, each of the at least two groupings representingat least one combination of at least one transport format and at leastone radio condition, selecting a signature from one of the at least twogroupings, the selection according to one of the representedcombinations and requesting access to the network using the selectedsignature.

It is contemplated that each of the at least one radio conditionincludes one of required uplink transmit power, reception quality ofdownlink signals, uplink interference, available power headroom and ananticipated difference between maximum allowed uplink transmit power anduplink transmit power. It is further contemplated that no specificcombination of at least one transport format and at least one radiocondition is represented by both of the at least two groups

It is contemplated that the method further includes receiving anindication of the at least two groupings of signatures. It is furthercontemplated that the method further includes receiving a responseacknowledging receipt of the access request, the response includingresources for accessing the network and transmitting data using theresources.

It is further contemplated that selecting a signature from one of the atleast two groupings includes determining an amount of data to transmitand allowable power headroom. It is further contemplated thatdetermining an amount of data to transmit includes at least one ofdetermining alternate message sizes for transmitting data and removingoptional information from the data.

It is contemplated that the method further includes not receiving aresponse acknowledging receipt of the access request within a specifiedamount of time and requesting access to the network again using asignature re-selected from one of the at least two groupings accordingto one of the represented combinations. It is further contemplated thatthe signature is re-selected from one of the at least two groupingsaccording to whether a represented combination of at least one transportformat and at least one radio condition can accommodate an increase intransmission power of the access request.

It is contemplated that re-selecting a signature from one of the atleast two groupings includes determining an amount of data to transmitand allowable power headroom. It is further contemplated thatdetermining an amount of data to transmit includes at least one ofdetermining alternate message sizes for transmitting data and removingoptional information from the data.

It is contemplated that the method further includes not receiving aresponse acknowledging receipt of the access request within a specifiedamount of time and requesting access to the network again using theselected signature. It is further contemplated that the method furtherincludes receiving a response acknowledging receipt of the accessrequest, the response including resources for accessing the network andan indication that the transmission power of the access request washigher than necessary and transmitting data using the resources, thedata transmitted at a power that is lower than the power obtained byapplying an offset to the transmission power of the access request, theoffset identified by a transport format represented by the grouping fromwhich the signature was selected.

It is contemplated that two groupings are identified, each groupingincluding signatures, and requesting access to the network includestransmitting a preamble according to the selected signature. It isfurther contemplated that each of the at least one transport formatidentifies a modulation and coding scheme, a number of resource blocksand a maximum payload.

In another aspect of the present invention, a method of establishing acommunication link between a mobile terminal and a network is provided.The method includes identifying at least two groupings of signatures foraccessing the network, each of the at least two groupings representingat least one combination of at least one transport format and at leastone radio condition, receiving an access request from the mobileterminal, identifying one of the at least two groupings to which asignature used to transmit the access request belongs. Preferably, themethod further includes allocating resources to the mobile terminalaccording to the identified grouping.

In another aspect of the present invention, a mobile terminal forestablishing a communication link with a network is provided. The mobileterminal includes a transmitting/receiving unit transmitting an accessrequest to the network, a display unit displaying user interfaceinformation, an input unit receiving inputs from a user and a processingunit identifying at least two groupings of signatures for accessing thenetwork, selecting a signature from one of the at least two groupingsand controlling the transmitting/receiving unit to request access to thenetwork by generating an access request message using the selectedsignature, wherein each of the at least two groupings represents atleast one combination of at least one transport format and at least oneradio condition and the selection of the signature is according to oneof the represented combinations.

It is contemplated that each of the at least one radio conditionincludes one of required uplink transmit power, reception quality ofdownlink signals, uplink interference, available power headroom and ananticipated difference between maximum allowed uplink transmit power anduplink transmit power. It is further contemplated that no specificcombination of at least one transport format and at least one radiocondition is represented by both of the at least two groups.

It is contemplated that the transmitting/receiving unit receives anindication of the at least two groupings of signatures. It is furthercontemplated that the transmitting/receiving unit receives a responseacknowledging receipt of the access request, the response includingresources for accessing the network, and the processing unit controlsthe transmitting/receiving unit to transmit data using the resources.

It is contemplated that the processing unit selects the signature fromone of the at least two groupings by determining an amount of data totransmit and allowable power headroom. It is further contemplated thatthe processing unit determines the amount of data to transmit by atleast one of determining alternate message sizes for transmitting dataand removing optional information from the data.

It is contemplated that the processing unit controls thetransmitting/receiving unit to request access to the network again uponnot receiving a response acknowledging receipt of the access requestwithin a specified amount of time, the access request performed using asignature re-selected from one of the at least two groupings accordingto one of the represented combinations. It is further contemplated thatthe processing unit re-selects the signature from one of the at leasttwo groupings according to whether a represented combination of at leastone transport format and at least one radio condition can accommodate anincrease in transmission power of the access request.

It is contemplated that the processing unit re-selects the signaturefrom one of the at least two groupings by determining an amount of datato transmit and allowable power headroom. It is further contemplatedthat the processing determines the amount of data to transmit by atleast one of determining alternate message sizes for transmitting dataand removing optional information from the data.

It is contemplated that the processing unit controls thetransmitting/receiving unit to request access to the network again uponnot receiving a response acknowledging receipt of the access requestwithin a specified amount of time, the access request performed usingthe selected signature. It is further contemplated that thetransmitting/receiving unit receives a response acknowledging receipt ofthe access request, the response including resources for accessing thenetwork and an indication that the transmission power of the accessrequest was higher than necessary, and the processing unit controls thetransmitting/receiving unit to transmit data using the resources, thedata transmitted at a power that is lower than the power obtained byapplying an offset to the transmission power of the access request, theoffset identified by a transport format represented by the grouping fromwhich the signature was selected.

It is contemplated that two groupings are identified, each groupingincluding signatures, and the processing unit controls thetransmitting/receiving unit to request access to the network bygenerating a preamble according to the selected signature. It is furthercontemplated that each of the at least one transport format identifies amodulation and coding scheme, a number of resource blocks and a maximumpayload.

In another aspect of the present invention, a network for establishing acommunication link with a mobile terminal is provided. The networkincludes a receiver receiving an access request from the mobile terminaland a controller identifying at least two groupings of signatures foraccessing the network, each of the at least two groupings representingat least one combination of at least one transport format and at leastone radio condition and identifying one of the at least two groupings towhich a signature used to transmit the access request belongs.Preferably, the controller further allocates resources to the mobileterminal according to the identified grouping.

These and other embodiments will also become readily apparent to thoseskilled in the art from the following detailed description of theembodiments having reference to the attached figures, the invention notbeing limited to any particular embodiments disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. Features, elements, and aspects of the invention that arereferenced by the same numerals in different figures represent the same,equivalent, or similar features, elements, or aspects in accordance withone or more embodiments.

FIG. 1 illustrates a block diagram illustrating network structure of anevolved universal mobile telecommunication system (E-UMTS).

FIG. 2 illustrates a block diagram depicting architecture of a typicalE-UTRAN and a typical EPC.

FIG. 3( a) illustrates the user-plane protocol for the E-UMTS.

FIG. 3( a) illustrates the control-plane protocol stack for the E-UMTS

FIG. 4 illustrates a Structure of the physical channel.

FIG. 5 illustrates a Random Access procedure for E-UTRAN initial access.

FIG. 6 illustrates a random access procedure according to the presentinvention.

FIG. 7 illustrates a block diagram of a mobile station (MS) or accessterminal (AT) according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. The present invention is directed to a RACH initial accessprocedure in a UE.

The present invention proposes a method to allow an accurate choice ofthe UL transport format. The new method allows the UE to determine byitself whether a certain transport format may be used for thetransmission of message 3 in FIG. 5 prior to the first preambletransmission and prior to the power ramping.

The UE determines the transmit power for message 3 in FIG. 5 based onthe transmit power of the preamble that has been detected by the eNB. Itis clear that a minimum SNR is necessary for the successful transmissionof an UL message, such as message 3 in FIG. 5. At the same time, it isnecessary that the preamble, such as message 1 in FIG. 5, be receivedwith a certain SNR in order to be considered as successfully received bythe NodeB.

The eNB knows the SNR required for successful detection of the preamblesince the SNR necessary for message 3 for each available transportformat is also known by the eNB. The eNB can indicate an offset fortransmission of message 3 compared to the transmission power of thepreamble, the offset indicated even before the preamble is detected.

The present invention takes into account more aspects of the potentialprocedure for the NSRA and considers how the information included inmessages may be reduced through linking the physical procedure and theMAC behavior while still conveying the necessary information.

A fixed or broadcast margin may be used as the offset relative to theestimated initial preamble transmission power. This is possible becausethe UE knows the currently used transmit power for the preamble, themaximum available or allowed transmit power. Alternatively, the UE mayre-evaluate which transport format may be transmitted prior to eachtransmission of a preamble, assuming that the eNB detects the preamble.

According to the present invention, it is essentially the UE thatdetermines which of the available transport formats are available fortransmission before each transmission of the preamble. This reducessensitivity to an erroneous estimation of the necessary transmit powernecessary for detection of the preamble.

A UE would then only determine a transport format that it is able totransmit. The determination is made according to the transmit power ofthe preamble that the UE will use, the difference between preambletransmit power and the required power for transmission of message 3 asindicated by the eNB, and the maximum available or allowed UE Transmitpower.

The eNB need not check whether the UE transmit power is sufficient whena UE indicates a signature corresponding to a certain transport formatfor transmission. This is because the detection of the UE alreadyimplies that the UE transmit power and the uplink channel quality issufficient to transmit the required transport format.

Therefore, the only information that the signature must indicate is thetransport format that the UE requests to use and further information,such as CQI or path loss, need not be coded in the preamble in order todetermine the possible transport formats for transmission of message 3.Furthermore, the eNB may indicate an additional offset in message 2 forthe transmission of message 3 compared to the transmission power of thepreamble if the transmit power chosen by the UE results in a higher SNRin the eNB than is needed for detection. It is beneficial to transmitthe uplink message in vicinity of the preamble from a frequency point ofview in order to ensure that the same channel is used for thetransmission of the message.

FIG. 6 illustrates a random access procedure according to the presentinvention. As illustrated in FIG. 6, the necessary information for thecalculation of the preamble is gathered in steps S10 to S40 in order toensure detection of the initial preamble and prepare a message, if any,for transmission.

The information that is needed in the UE includes any combination ofuplink interference, pilot transmit power, required SNR and possiblyadditional offsets in order to calculate the necessary preamble transmitpower based on the measured received pilot receive power as well asallowed transport formats for transmission of a RACH message in theuplink, offsets related to the power with which the preamble has beentransmitted for each transport format, and information related to powerramping for successive preamble transmissions. Transport formats shouldinclude at least the available payload size, but other information, suchas coding type and necessary time/frequency resources, may be included.

One additional margin, or a specific margin per transport format, isnecessary if the estimation of the allowed transport formats for theuplink is done only once prior to the transmission of the initialpreamble. This allows the UE to determine whether a transport format maybe transmitted including a margin for eventual power ramping based onthe estimated initial preamble transmission power.Signature/time/frequency resources associated with each transport formatshould also be made available, specifically if no message needs to betransmitted.

The needed information may either be broadcast on the system informationin a cell or fixed in a standard. The order in which steps S10 to S40are performed is interchangeable.

The UE determines in step S50 which transport formats may be used basedon the transmission power that will be used for the transmission of thepreamble. This determination may be performed once before thetransmission of the first preamble, with a set of possible transportformats identified by the UE according to the transport formats forwhich the following equation is fulfilled:Offset_(TFi)+Margin_(TFi) <P _(Max) −P _(Preamble)

Alternatively the determination may be performed before eachtransmission of the preamble. In this case, the available set ofpossible transport formats may change during the procedure if thetransmit power is increased or if parameters, such as the uplinkinterference value, change.

The UE then chooses from the possible transport formats the transportformat that allows the largest version of the message that should betransmitted. The transport format that requires the least transmitpower, adds the least padding, or uses the least time/frequencyresources may be chosen if several transport formats are possible.

It is not necessary that the possible transport formats be determinedprior to choosing the transport format that best suits the message size.The suitable transport formats may be determined first and then which ofthe suitable transport formats may be used is determined based on theinitial power estimation.

As illustrated in step S60, the RACH procedure is ended unsuccessfullyif no transport format can be chosen that allows transmission of atleast the smallest version of the message based on the determinedpreamble transmit power. As illustrated in step S70, the UE then selectsa signature and a time/frequency resource for transmission from a setcorresponding to the selected transport format if a suitable transportformat has been identified.

Different transport formats might be coded on the same group ofsignatures, for example, if the time/frequency resources required arethe same. A specific set of signatures and time/frequency resourcescould be reserved for when no message part is supposed to be transmittedand a UE that has no message to be transmitted can choose a signaturefrom this set.

It is determined in step S80 whether the UE receives an ACK. The ACK mayinclude a timing advance value and an uplink resource assignment.

The UE transmits the message using the determined transport format, asillustrated in step S100, if an ACK is received. An additional offset,such as Off_(overshoot), may be included in the ACK if the eNB detectsthat the transmission power of the preamble exceeds the threshold. Inthis case, the message is sent with a power determined according to thefollowing equation:P _(Tx) =P _(Preamble)+Offset_(TFi)−Off_(Overshoot)

The UE determines whether to stop the procedure unsuccessfully orcontinue with the preamble transmission at another occasion, asillustrated in step S90, if a negative acknowledgement or noacknowledgement is received from the eNB. If it is determined tocontinue with the preamble transmission at another occasion, the UE willincrease its preamble transmission power if applicable and/or change thefrequency resources used for the transmission of the next preamble, asillustrated in step S110. Depending upon whether the UE determines theuplink transport format at each transmission of the preamble or whetheruplink transport format is determined only once for the transmission ofthe first preamble, the process then returns to either step S50 or S0.

Two possible methods are contemplated. The UE may determine a transportformat for use based on the message size and transport formatinformation and associated offsets and, possibly, a margin compared tothe transmission power of the initial or the next preamble, withtransport format information and offset information either broadcast onsystem information or fixed in a standard. On the other hand, the UE maychoose the signature and time/frequency resources for the preambletransmission based on a chosen transport format, where each transportformat corresponds to a set of signatures and time/frequency resourcesthat are either fixed in a standard or broadcast by the eNB and fromwhich the UE chooses randomly or based on other criteria. Differenttransport formats may use the same set of signatures if, for example,different transport formats require the same time/frequency resources.

FIG. 7 illustrates a block diagram of a mobile station (MS) or accessterminal 2. The AT 2 includes a processor (or digital signal processor)110, RF module 135, power management module 105, antenna 140, battery155, display 115, keypad 120, memory 130, SIM card 125 (which may beoptional), speaker 145 and microphone 150.

A user enters instructional information, such as a telephone number, forexample, by pushing the buttons of a keypad 120 or by voice activationusing the microphone 150. The microprocessor 110 receives and processesthe instructional information to perform the appropriate function, suchas to dial the telephone number. Operational data may be retrieved fromthe Subscriber Identity Module (SIM) card 125 or the memory module 130to perform the function. Furthermore, the processor 110 may display theinstructional and operational information on the display 115 for theuser's reference and convenience.

The processor 110 issues instructional information to the RF module 135,to initiate communication, for example, transmits radio signalscomprising voice communication data. The RF module 135 comprises areceiver and a transmitter to receive and transmit radio signals. Anantenna 140 facilitates the transmission and reception of radio signals.Upon receiving radio signals, the RF module 135 may forward and convertthe signals to baseband frequency for processing by the processor 110.The processed signals would be transformed into audible or readableinformation outputted via the speaker 145, for example. The processor110 also includes the protocols and functions necessary to perform thevarious processes described herein.

As the present invention may be embodied in several forms withoutdeparting from the spirit or essential characteristics thereof, itshould also be understood that the above-described embodiments are notlimited by any of the details of the foregoing description, unlessotherwise specified, but rather should be construed broadly within itsspirit and scope as defined in the appended claims. Therefore, allchanges and modifications that fall within the metes and bounds of theclaims, or equivalence of such metes and bounds are intended to beembraced by the appended claims.

The foregoing embodiments and advantages are merely exemplary and arenot to be construed as limiting the present invention. The presentteaching can be readily applied to other types of apparatuses.

The description of the present invention is intended to be illustrative,and not to limit the scope of the claims. Many alternatives,modifications, and variations will be apparent to those skilled in theart. In the claims, means-plus-function clauses are intended to coverthe structure described herein as performing the recited function andnot only structural equivalents but also equivalent structures.

What is claimed is:
 1. A method of establishing a communication linkbetween a mobile terminal and a network, the method comprising:identifying, by the mobile terminal, a first preamble grouping and asecond preamble grouping for accessing the network via a random accesschannel (RACH), wherein the first and second preamble groupings areidentified according to information received from the network;selecting, by the mobile terminal, a preamble from the first or secondpreamble grouping according to at least one radio condition and anamount of data which will be transmitted by the mobile terminal; andrequesting, by the mobile terminal, access to the network by sending anaccess request using the selected preamble.
 2. The method of claim 1,wherein the at least one radio condition comprises required uplinktransmit power, reception quality of downlink signals, uplinkinterference, available power headroom or an anticipated differencebetween maximum allowed uplink transmit power and uplink transmit power.3. The method of claim 1, wherein the information including anindication of a size of the first preamble grouping.
 4. The method ofclaim 1, further comprising: receiving a response acknowledging receiptof the access request, the response comprising resources for accessingthe network; and transmitting data using the resources.
 5. The method ofclaim 1, further comprising determining the amount of data that will betransmitted by the mobile terminal by at least determining alternatemessage sizes for transmitting the data or removing optional informationfrom the data.
 6. The method of claim 1, further comprising:re-selecting a preamble from the first or second preamble grouping whena response acknowledging receipt of the access request is not receivedwithin a specified amount of time; and requesting access to the networkagain using the re-selected preamble.
 7. The method of claim 6, whereinthe preamble is re-selected according to the amount of data that will betransmitted by the mobile terminal and the at least one radio condition.8. The method of claim 7, further comprising determining the amount ofdata that will be transmitted by the mobile terminal by at leastdetermining alternate message sizes for transmitting the data orremoving optional information from the data.
 9. The method of claim 1,further comprising: receiving a response acknowledging receipt of theaccess request, the response comprising resources for accessing thenetwork and an indication that a transmission power of the accessrequest was higher than necessary; and transmitting data using theresources at a power that is lower than a power obtained by applying anoffset to the transmission power of the access request, the offsetidentified by a transport format represented by the first or secondpreamble grouping from which the preamble was selected.
 10. A method ofestablishing a communication link between a mobile terminal and anetwork, the method comprising: grouping, by the network, one or morepreambles according to a requested amount of radio resources;transmitting, by the network, grouping information that is used toselect at least one preamble group among a plurality of preamble groups;and receiving, by the network, at least one preamble that was selectedaccording to at least one radio condition and an amount of data to betransmitted by the mobile terminal, wherein the at least one preamble isfor accessing the network via a random access channel (RACH).
 11. Themethod of claim 10, wherein the at least one radio condition comprisesrequired uplink transmit power, reception quality of downlink signals,uplink interference, available power headroom, or an anticipateddifference between maximum allowed uplink transmit power and uplinktransmit power.
 12. The method of claim 10, wherein the groupinginformation includes an indication of a size of a first preamble group.13. The method of claim 10, further comprising transmitting a responseacknowledging receipt of the at least one preamble, the responsecomprising resources for accessing the network.
 14. The method of claim10, wherein the amount of data to be transmitted is determined by atleast determining alternate message sizes for transmitting the data orremoving optional information from the data.